1. Field of the Invention
This invention relates to apparatus for separating solids such as plastic pellets, from fluids or liquids mixed therewith to form a slurry. More particularly, the present invention is concerned with improvements in stationary dewatering screens for the purpose of removing a large portion of a liquid from a liquid-solid slurry.
2. Description of the Prior Art
One of the problems associated with separating liquids from solids by the use of a separating screen involves the blockage of the screen with solid matter which accumulates within the pores of the separating screen and thus greatly reduces the separation efficiency. U.S. Pat. No. 1,525,449, issued Feb. 10, 1925 to Johnson, attempts to solve this problem by directing a current of the materials to be strained directly across the face of the strainer whereby the accumulation of solid matter is prevented. The Johnson patent utilizes a strainer in the form of a cylinder and provides a turbine mixer positioned at about the center of the cylinder for directing a current of materials to be strained along substantially the entire face of the cylindrical surface, thus inserting rapid straining action and also preventing accumulation of solid matter on the strainer. The solution to the problem of clogged screens proposed in the Johnson patent, however, just creates a further problem since the moving turbine structure of the patent would be costly to assemble and more than likely would require constant maintenance. Another problem which is not recognized by Johnson is that by forcing the material against the screen, solid matter which would not ordinarily pass through the pores of the screen may be directed at such force so as to be driven into the pores of the screen. U.S. Pat. No. 2,133,974, issued Oct. 25, 1938 to Cowles, discloses a separating apparatus adapted for the treatment of solids suspended or entrained in a liquid. One of the objects of the invention of the Cowles patent is to provide a relatively small inexpensive apparatus which will perform an efficient separation without the use of moving parts. The Cowles patent provides a plurality of blades set edgewise to the flow of material entering a separation chamber with the faces of the blades parallel to the axis of flow. Large pieces of solid matter which do not pass through the space between the blades impinge on the blades and are deflected out of the path of flow, sliding along the blades under the combined influence of the force of the flow and gravity. A separating device similar to the Cowles patent is disclosed in U.S. Pat. No. 2,090,997, issued Aug. 24, 1937 to French for the purpose of eliminating refuse such as leaves, twigs, etc. from the water passing from the eave trough of a roof of a building to a storage tank or sewer. The French patent also utilizes a baffle plate which directs the refuse such as the leaves, twigs, etc. with a flow of water, the water passing through openings in the baffle plate while the refuse is directed to an opening out of the flow path of the water. The dewatering screen of the present invention is unlike the separating apparatus of French and Cowles since in the present invention means are provided to deflect the slurry from the incoming flow path into a dewatering screen in which the solid particles too large to pass through the screen continue in a flow path parallel and below the incoming slurry due to the force of gravity. Also of interest is Vernon E. Dudley U.S. Pat. No. 3,458,045 which discloses a grate device extending across the flow path of a downwardly angled duct section.